The present invention relates to apparatus for measuring the light transmissivity (transparency) of exposed and developed photographic films or the like. More particularly, the invention relates to apparatus for measuring the light transmissivity of exposed and developed film frames prior to the making of prints of such frames in a color printing or like copying machine. Still more particularly, the invention relates to improvements in apparatus for measuring the transmissivity of peripherally disposed background portions of originals to be copied, i.e., of portions which surround the centrally disposed subject portion of an original.
It is already known to depart from integral light measurement of originals, i.e., to control the operation of automatic photographic printers on the basis other than the neutral grey principle. Reference may be had to U.S. Pat. No. 3,708,676 granted Jan. 2, 1973 to Huboi et al. As a rule, one attempts to collect or group together those originals which exhibit identical or similar distribution of density, i.e., which can be exposed with the same setting of controls at the copying station. U.S. Pat. No. 3,790,275 granted (Feb. 5, 1974 to Huboi et al. proposes to use discrete radiation sensitive devices for receiving radiation from the upper portion of the peripheral zone of an original, from the lower portion of the peripheral zone, and from the centrally disposed portion of the original. The patentees further propose to determine the average light transmissivity of the entire original to allow for grouping of the original with originals exhibiting the same or similar average transmissivity.
The means for measuring the transmissivity of originals includes an optical system which images the original onto a raster of radiation-sensitive photoelectric transducers which transmit signals to a computer. The central portion of the raster includes a plurality of radiaiton sensitive devices which sense radiation derived from a plurality of discrete sub-portions of the subject portion of the original. This enables the apparatus to ascertain that discrete sub-portion of the central portion of the original having the greatest or maximum transmissivity. The patented apparatus is incapable of ascertaining the total light transmissivity of originals.
Another conventional apparatus employs a lens which projects the image of the original into the plane of a rotating diaphragm. The diaphragm has a plurality of different holes (including U-shaped holes) which allow light passing therethrough (i.e., light which has passed through different portions of the original including the upper and lower portions of the peripheral zone) to impinge upon a photoelectric transducer. Such apparatus exhibit the drawback that signals denoting the characteristics of different portions of an original are produced at timely spaced intervals, i.e., the signals must be stored prior to transmission to the evaluating circuit which must receive all signals at the same time. Moreover, the apparatus are complex and expensive because they employ moving parts and must be equipped with means for synchronizing the movement of diaphragm with the operation of signal storing means.